Gas turbine engine blades contain channels which lead from an exterior surface to an interior plenum. An example is shown in FIG. 1, wherein a blade 2 contains a plenum 3 to which channels 6 connect and lead to an external surface 9. In use, pressurized air is applied to the plenum 3 causing cooling airstreams 12 to flow through the channels 6, thereby absorbing heat from the walls of the channels 6, as well as from the surface 9 of the blade 2, thereby cooling the blade 2.
In order to function properly, the channels 6 must be constructed to a known configuration because the distribution of airflow must be controlled in order to achieve proper cooling. Restated, the channels 6 must not be blocked, not even partially. However, inspection of channels 6 to detect blockages from the external surface 9 is difficult. One reason is that they are very small, a typical diameter being 12 mils (0.3 mm), and thus it is nearly impossible to insert a diameter measurement gage into the channels 6.